1. Field of the Invention
The present invention relates to improvements of a liquid leakage sensor and a liquid leakage detecting system for detecting a leakage of an electrically conductive liquid such as a water, an acid solution, or an alkaline solution, etc., and a leakage of a liquid having an insulating property such as a super pure water, an organic solution of an alcohol, a thinner, or a benzine, etc.
2. Background Art
Conventionally, a liquid is supplied through piping in a facility of a factory, etc. However, since the number of joints connecting these pipes is very numerous, there are many cases in which a liquid is leaked from these joints. Therefore, an operator had to monitor a leaking liquid at all times according to the kinds of liquids. As such a conventional liquid leakage sensor, a leakage sensor based on measuring an electrical conductance between electrodes is known for determining a leakage from an impedance change, and a leakage sensor based on measuring a volume of the liquid is also known in which the specified quantity of the liquid is checked whether accurately supplied or not. Further, a patent literature 1 describes an optically measuring technique of a liquid leakage sensor. In this art, a light is projected from a light-emitting portion (light source) to a filter on which the opaque filter changes into a transparent state by absorbing a leaked liquid. Therefore the liquid leakage can be accurately detected based on measuring the amount of a received light through the transmitting filter or from a reflecting light on the above filter. In these conventional leakage sensors, abnormal status-conditions of these sensors are generally displayed on an alarming display-means such as an LED, etc. and digitally issued as an external output through a contact signal, etc., immediately after detecting a leaking liquid or detecting mal-installation conditions of the sensor at a predetermined spatial position.
On the other hand, a patent literature 2 describes a liquid leakage monitor system wherein desired information such as an impedance between the electrodes of a child leakage sensor, etc. are communicated among plural child devices and a parent device, and these information are displayed on a display means of the parent device after these information are processed in the parent device, or transparently passed. In the patent literature 2, after it is determined that an abnormal condition of a child sensor device is detected, an alarm signal of this leakage sensor is displayed on a screen image and/or on a recording means, and further reported by an audio means such as a buzzer, etc.
By the way, (A) in case of detecting a leaking liquid such as a cleaner/a solvent, for example, a liquid having a low surface tension of 6×10−2 N/cm or less at 20° C., a leaking liquid 2a is diffusing on a floor while forming a very thin layer as shown in FIG. 6B, further, in case of detecting a leaking liquid having a low surface tension of 3×10−2 N/cm or less at 20° C. such as a low molecular chlorofluorocarbon (CFCs), a halon, etc. not including a chlorine or a bromine, the leaking liquid is rapidly diffusing uniformly with the thinner film layer having 0.5 mm or less in thickness d1, and easily permeating into an air gap portion of a very narrow distance of 0.1 mm or less. In this very narrow air gap, the leaking liquid is at first permeating into the clearance d2 (<d1) between a case holder of a sensor main body and a floor surface (FIG. 6C). So that it takes a long time for the leaking liquid to diffuse over the upper surface of the holder. Consequently, the following problems cannot be resolved, that is, a small amount of a leaking liquid cannot be detected at all, or too many times are wasted until a detection of a bit of a liquid is started.
(B) Further, in the conventional liquid leakage sensor, a wired-OR logical operation for alarming external-outputs of plural sensors is conveniently performed, and these digital outputs are commonly connected and inputted into a single port of the sequencer, or a parent device, etc. at each specified group unit. Then, after detecting abnormal conditions of a leakage sensor, a common warning signal is issued from the sequencer or the parent device. After issuing the warning signal related to the plural leakage sensors, a maintenance problem of a system in a plant occurs, that is, an operator cannot identify quickly where is the error-activated sensor in order to spatially access and repair the abnormal condition among commonly connected plural sensors. Furthermore, from a view point of the environmental working-conditions, liquid leakage sensors are generally installed at the lowermost portion of a system such as a floor surface, or a liquid storing pan, etc. and various system components are placed at an upper space of the system, therefore, another maintenance problem also occurs in which a light emitting-type alarm display-means such as LED, etc. attached to the liquid leakage sensor itself is functioning very difficult to visually recognize the location of an error-activated sensor among plural sensors, and it is generally difficult to identify easily the location of a leak-activated sensor through the display means installed at the lowermost portion of the system.
(C) Moreover, in the liquid leakage detecting system of the patent literature 2, etc., there are generally existing no relations at all between an operator for installing the liquid leakage sensors and an operator for maintaining and monitoring the system of a plant, etc. As for the operator installing the leakage sensors, it is only required to install accurately all of many commonly connected sensors at the given spatial-positions within a short time. Therefore, as a desk theory, it is possible for the operator to require a registering operation in which each installation location of a sensor is registered into a monitor system one by one. However, in a practical sense, it is impossible to require such a registering operation for one operator wherein he must accurately install more than forty sensors at each specified location, then execute wiring operation without any mistakes, at next step register and verify each installation location of respective sensor accurately. In a system installation, if plural workers are admitted in the installation work of the leakage sensors, a purchase price of the sensors is unnecessarily sky-rocketed. Therefore, for an operator of the sensor installation, the technique disclosed in the patent literature 2 is completely useless in a practical sense.
Furthermore, in the technique of the patent literature 2, the system is constructed such that a warning signal is displayed in a display of the parent device after processing is done on the parent, or raw data are transmitted transparently throughout the system. Therefore, when any system failure is occurred in the parent, another problem is also invited wherein no warning signals can be issued from the parent while detecting any error conditions in a normal child sensor.
In addition, the technique of the patent literature 2 discloses a system wherein a liquid leakage error is announced in a form of voice messages provided from a warning means in the parent after processing in the parent, or raw data are transmitted transparently throughout the system. Therefore, it is essential that the spatial positioning information concerning the error-activated sensor should be contained in the contents of the voice warning messages. And as for the operator for maintaining or monitoring the system of a plant, it is also essential that the announced voice warning messages must be accurately heard by the operator, then the location of the detecting error must be correctly understood, and the spatial position of the error-activated sensor must be uniquely identified. However, in the severe job/field site conditions, a frequent use of a dispatch staff member and frequently repeated personnel exchanges, there are almost no times/costs spending for an education of teaching about the installation positions of the liquid leakage sensors, etc. Therefore, another problem is also invited in the alarming system of the patent literature 2 wherein as for a new-coming operator or an operator insufficient in a memory power/a learning ability, the announcing system consisting of warning voice messages is completely useless in order to repair or exchange the error-activated leakage sensor.
(D) When a liquid leakage sensor and its warning means are integrally formed, it is desirable that the total height of a sensor from a floor surface to its top is as low as possible. Because a liquid leakage sensor is generally installed at a narrow lower space near a floor surface and can be easily interfered with a passing space of an operator.
Patent literature 1: JP-B-4-70572
Patent literature 2: JP-A-2002-350275